This proposal describes the design and testing of new enzyme-based amperometric sensors for the neurochemically important species, choline, acetylcholine and glutamate. In these devices, the electrical communication between the flavin redox centers of an oxidase and an electrode is achieved via a network of donor-acceptor relays chemically bound to a highly flexible polymer. Because the electron transfer mediators are covalently attached to an insoluble polymer and cannot diffuse away from the electrode, these sensors should be suitable for implantation, and thus would be useful for in vivo neurochemical research. The proposed research plan concerns the development of highly sensitive and selective micro-biosensors which can be used as implantable probes or in combination with conventional microdialysis techniques. The sensors should permit detection of these neurochemicals over much shorter time scales than presently available assays.